There are a number of surgical procedures that require a fixation of portions of the spine with respect to one another. Typically, bone screws or bolts are employed in the fixation of the spine wherein the bone screws or bolts are implanted in a surgical procedure involving the formation of one or more surgical openings in adjacent portions of the spine, for implanting the threaded bone bolts or screws into the vertebrae. Structures such as longitudinal rods or plates extend between the various spine members and are connected to the implanted bone bolts or screws with connector devices.
Connectors for attaching the rods or plates to vertebrae of a spinal column are known in the art. However, current bolt to rod connectors do not allow for adjustability in multiple planes in order to better conform to the anatomical structure of the patient and to eliminate initial stresses on the spinal fixation construct. In spinal surgery that requires distraction, compression, and rotation of the construct to obtain proper assembly, stresses are put on the component parts of existing spinal fixation systems and on the vertebral column, which are not designed to accommodate stresses much higher than those encountered during normal patient activity. By reducing the initial stresses on the construct and the vertebral column, the connector of the present invention allows the entire strength of the connector to be reserved for stresses encountered during patient activity. This provides a spinal construct for a non-compliant patient with activity limitations that is less likely to fail than one with initial high stresses.
Additionally, some existing fixation systems, such as U.S. Pat. Nos. 5,209,752 and 5,176,697, require lateral or medial approaches to assemble and tighten the construct which causes complicated surgical procedures due to the soft tissues that are lateral to the incision. Potential damage can also occur to neurological elements that are medial to the construct.
Current spinal fixation systems, for example such as those shown in U.S. Pat. Nos. 4,719,905 and 5,296,014, also have many pieces to assemble and lack anatomical adjustability which results in long surgeries that put increased stresses on the surgeon and surgical staff. Long surgical times increases patient morbidity due to blood loss and stresses of anesthesia. The large number of pieces in current fixation systems require hospitals to keep large inventories which is difficult during the present time of medical cost containment.
Accordingly, it is a principal object of the present invention to provide a simple and fast way to attach a spinal rod to the spine. The "single piece" (4 pieces pre-assembled) connector of the present invention facilitates rapid assembly during implantation of the fixation construct. This reduces operating time, blood loss and complications which makes the present invention more appealing to surgeons who will spend less time assembling and adjusting spinal fixation constructs in the operating room.
It is another object of the present invention to provide a spinal fixation connector that has a wide range of adjustability to accommodate a range of anatomical variations and to eliminate the initial stresses on the spinal fixation construct.
It is a further object of the present invention to provide a connector that is secured by means of a single set screw that is accessed from a posterior approach. This provides fewer screws for the surgeon to tighten and makes the securing and tightening of the spinal construct easier to access.
It is a further object of the present invention to provide a connector that allows adjustment in four axes of movement that includes a cephalad/caudal direction, a medial/lateral direction and angulation in a sagittal plane and a transverse plane when the assembly is being implanted in a patient.